The present invention generally relates to intravascular catheters. More specifically, the present invention relates to low profile intravascular micro-catheters.
Intravascular catheters are used in a wide variety of relatively non-invasive medical procedures. Such intravascular catheters may be used for diagnostic or therapeutic purposes. Generally, an intravascular catheter allows a physician to remotely perform a medical procedure by inserting the catheter at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient""s vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature.
Intravascular catheters typically have a radiopaque portion and are guided through the patient""s vascular system with the assistance of x-ray fluoroscopy. A physician may manipulate the proximal end of the catheter and fluoroscopically monitor the corresponding movement of the distal end of the catheter. Thus, it is desirable that the catheter be sufficiently radiopaque along its length and particularly at its distal end to enable the physician to clearly monitor the progress of the catheter as it is being advanced from the vascular access site to the vascular target site.
After the intravascular catheter has been navigated through the patient""s vascular system with the distal end thereof adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. Frequently, diagnostic and therapeutic techniques require the infusion of fluids or other materials through the catheter. For example, it may be desirable to deliver an embolic material (e.g., embolic gel, coil, etc.) through the catheter to embolize an aneurysm, shunt, or the like, inject radiopaque contrast media through the catheter to provide enhanced fluoroscopic visualization for diagnostic purposes, or inject pharmaceutical solutions (i.e., drugs) to the target site for therapeutic purposes. In order to maintain a fluid path in the catheter for such purposes, it is desirable that the catheter be sufficiently resistant to kinking. In addition, because such fluids are typically delivered under pressure, it is also desirable that the catheter be sufficiently resistant to bursting.
To satisfy some of these desirable features, prior art intravascular catheters have utilized a reinforcement structure such as a braid or coil disposed between an inner lubricious tubular layer and an outer flexible tubular layer. A braid reinforcement structure offers high resistance to bursting, and a coil reinforcement structure offers resistance to ovaling and kinking. Thus, an intravascular catheter may be kink resistant or burst resistant by utilizing a reinforcement structure such as a coil or braid.
It is also desirable that an intravascular catheter be relatively long and flexible because the distance between the access site and the target site is often in excess of 100 cm and is usually defined by a tortuous path. In addition, because the inside diameter of the vasculature at the target site is often less than 5 mm, it is also desirable that the intravascular catheter have a small profile. Accordingly, an intravascular catheter is preferably long, flexible, and thin.
To provide a relatively thin or small profile catheter, various collapsible and expandable shaft designs have been proposed. However, these designs are not suitable for the delivery of embolic material to remote target sites. Further, these designs do not offer a reinforcement structure in the expandable portion, which may compromise kink resistance and burst resistance as described previously. Examples of such prior art catheters may be found in U.S. Pat. No. 4,406,656 to Hattler et al., U.S. Pat. No. 5,618,267 to Palestrant, and U.S. Pat. No. 5,318,588 to Horzewski et al.
U.S. Pat. No. 4,406,656 to Hattler et al. discloses a venous catheter including a plurality of collapsible lumens formed from a material which is normally collapsed in a small cross-sectional area and which is further capable of expanding when fluid is flowing therein to a cross-sectional area which is much greater than that when collapsed. Each of the collapsible lumens defines a fluid passageway for the infusion of fluid therethrough. The sides of the collapsible lumen are made from a material having sufficient resiliency to expand outwardly as fluid flows through the passageway.
U.S. Pat. No. 5,618,267 to Palestrant discloses a collapsible infusion catheter formed of a normally flattened tube of flexible, collapsible plastic. The infusion catheter is initially in a collapsed configuration. During infusion, the catheter expands to a generally oval profile. The infusion catheter allegedly reduces the likelihood of clot formation, minimizes blood flow obstruction when the catheter is collapsed, and provides an expanded flow lumen for infusing fluids.
U.S. Pat. No. 5,318,588 to Horzewski et al. discloses a radially expandable intravascular catheter formed of an elastic material. The intravascular catheter may be expanded in the radial direction by inserting a diagnostic, therapeutic, or other device into the catheter lumen. With this arrangement, the catheter lumen is expanded by radial forces applied by physical contact with the device inserted into the lumen.
Among other deficiencies, none of these proposed catheter designs are particularly suitable for the delivery of embolic material to remote target sites. Further, none of these proposed catheter designs offer reinforced expandable portions.
The present invention overcomes these disadvantages by providing a method of delivering a therapeutic agent (e.g., an embolic material) to a vascular site using a catheter including a shaft having an expandable portion, preferably with a reinforcement structure. The catheter is navigated, at a first relatively small diameter, to the vascular site. Pressure is applied to the lumen of the shaft thereby expanding the expandable portion of the shaft from the first diameter to a second larger diameter, suitable for delivery of a therapeutic agent. The therapeutic agent is then delivered to the vascular site through the lumen of the catheter. The therapeutic agent is preferably disposed in the lumen of the shaft such that the expansion pressure is created, in part, by resistance of the therapeutic agent to flow through the lumen.
Preferably, the shaft expands predictably with pressure. For example, the first diameter may be maintained below a first threshold pressure. The second diameter may be established at a second threshold pressure and maintained above the second threshold pressure.
The present invention also provides an intravascular catheter having a reinforced tubular shaft, at least a portion of which is expandable. The shaft includes a lumen extending therethrough and an open distal end. The expandable portion is sufficiently expandable such that the shaft may expand from a first diameter to a second diameter upon increasing the pressure in the lumen of the shaft. Preferably, the expandable portion is sufficiently elastic such that the shaft may return to the first diameter upon decreasing the pressure in the lumen of the shaft. The expandable portion may be disposed at the distal end of the shaft, preferably in the form of a tapered tip.
The reinforcement structure may comprise, for example, a coil, a braid, a knit or an intermediate tube. In any instance, the reinforcement structure includes a plurality of circumferential elements having means for permitting an increase in the circumference. The circumference-increasing means may comprise, for example, a spring, an elastic segment, or slack in the circumferential element.
The reinforcement structure within the expandable portion may be disposed on or in a polymer tubular layer, or between two polymer tubular layers. The polymer layers are also sufficiently expandable to permit expansion of the shaft. Preferably, the polymer layer or layers permit relative movement of the circumference-increasing means. By permitting an increase in circumference, the reinforcement structure allows the shaft to expand from the first diameter to the second diameter.